The present invention relates to a method for increasing the braking effect in a motor vehicle with a hydraulic brake system, wherein an energy supply unit, which is used to increase the brake pressure in at least one wheel brake, is switched on when the brake pressure adjusted by the driver in a master brake cylinder reaches a first activation threshold value, which is determined depending on a detected vehicle deceleration.
When subjected to high thermal load, under the influence of saline solution and major wear, hydraulic brake systems exhibit a reduced effectiveness so that, even given a high initial pressure in the master brake cylinder that is adjusted by the driver, the brake system will not bring about sufficient deceleration of the vehicle. The reduced braking effect at high working temperatures of the brake system is referred to as ‘fading’.
In the cases illustrated hereinabove, the reduced braking effect of the vehicle brake system results, however, especially from a reduced coefficient of friction between the brake pads and the brake disc, so that a special rate of brake pressure is required in order to brake the vehicle effectively.
German published application DE 102 38 427 A1 discloses a method of the type referred to hereinabove, wherein in case of limited effectiveness of the vehicle brake, enabling of an energy source causes increase of the brake pressure or the brake force in the wheel brakes. A method of this type is also referred to as FBS function (FBS: Fading Brake Support).
The energy source, which is usually a pump, is activated in the FBS function when the initial pressure in the master brake cylinder adjusted by the driver exceeds an activation threshold, which is determined depending on the vehicle deceleration. Thus, the pump is switched on when the actual vehicle deceleration is by a defined value lower than the vehicle deceleration that is expected due to the adjusted initial pressure, with the brake system functioning properly.
It has shown that in car-trailer combinations consisting of a vehicle and a loaded unbraked trailer, frequent spurious releases of the FBS function are encountered, meaning the FBS function is activated although the brake system of the vehicle exhibits its normal braking power.
This is very disadvantageous for the driver of such a car-trailer combination because a considerably higher braking power is reached in a brake operation by way of the spurious releases of the FBS function than is expected and desired by the driver. The result is a major loss in comfort for the driver. In addition, unexpected abrupt braking of the vehicle can provoke rear end collisions.
In view of the above, an object of the invention is to overcome the illustrated shortcomings of the state of the art, and, in doing so, to prevent in particular spurious releases of the FBS function in car-trailer combinations consisting of a vehicle and a trailer.